1. Field of the Invention
The present invention relates to an LED lamp in which at least a portion of the radiation produced by an LED chip is subjected to a wavelength conversion with a phosphor.
2. Description of the Related Art
White LED lamps are recently under vigorous research and development. When LED chips are used as a lamp, blue-emitting LED chips are sometimes coated with a yellow-emitting phosphor to obtain color white that is suitable for illumination purposes (see Japanese Patent Publication No. 2998696, for example). In this manner, white light can be extracted as synthesized light by subjecting a portion of the radiation produced by the LED chips to a wavelength conversion with the phosphor. More specifically, a blue LED chip, made of gallium nitride (GaN), is coated with a phosphor such as YAG. In such an LED lamp, the blue LED chip produces an emission with a wavelength of about 450 nm, and the phosphor produces yellow fluorescence with a peak wavelength of about 550 nm on receiving that emission. Eventually, the emission and fluorescence mix with each other, thereby providing white light.
The present inventors completed an invention of dissipating the heat, generated by an LED chip, into a substrate by directly mounting the LED chip on the substrate and disclosed the invention in Japanese Laid-Open Publication No. 2004-172586. FIG. 3 is a cross-sectional view of the LED lamp 300 disclosed in Japanese Laid-Open Publication No. 2004-172586. In this LED lamp 300, an LED chip 12 provided on a substrate 11 is covered with a cylindrical resin portion 60 containing a phosphor. The cylindrical resin portion 60 is further covered with a second resin portion 61. The cylindrical resin portion 60 functions as an optical wavelength converting portion. And the light 62 is radiated outward through the second resin portion 61.
However, the present inventors discovered, as a result of further researches, that the luminous flux of the LED lamp changed significantly when the shape of the cylindrical resin portion 60, containing the phosphor, was changed.